The present invention relates to an SP location detector which detects patterns of scattered pilot (hereinafter called “SP”) signals dispersively disposed in received signals in predetermined patterns at ISDB-T (Integrated Services Digital Broadcasting-Terrestrial: Terrestrial Digital Broadcasting) or the like.
As described in patent documents 1 and 2 (Japanese Unexamined Patent Publication Nos. 2004-153811 and 2005-45664), a broadcast signal of ISDB-T is constituted of 13 OFDM (Orthogonal Frequency Division Multiplex) segments (hereinafter called simply “segments”) in television broadcasting and one or three segments in radio broadcasting. One segment corresponds to a bundle of a predetermined number of carriers (108 in a mode 1, for example) corresponding to each transmission mode and has a band of about 430 kHz. As the carriers, there are a control information carrier modulated in a predetermined modulation scheme and a data carrier which is modulated in a modulation scheme indicated by the control information carrier and transmits broadcast main information.
At one segment, each carrier is modulated based on each individual complex symbol (corresponding to a so-called IQ symbol that represents an orthogonal component of an information signal in the form of a real part and an imaginary part) for every symbol period or cycle (modulation cycle)) and multiplexed into one OFDM symbol, followed by transmission thereof. 204 OFDM symbols constitute one transmission frame.
FIG. 2 is a diagram showing a configuration example of a transmission frame of ISDB-T. In FIG. 2, carriers are shown so as to be arranged from left to right in increasing order of frequency, and OFDM symbols are shown so as to be arranged from top to bottom in order of time. One complex symbol c (n, k) that modulates a carrier k during a period of a symbol number n, is positioned at a cell at which the carrier and the OFDM symbol intersect. Accordingly, the present figure shows a sequence or arrangement of carriers each corresponding to the complex symbol (n, k) in frequency order and time order.
Symbols described as “SP” in FIG. 2 respectively indicate SP symbols corresponding to pilot symbols each indicative of a reference value used in signal equalization. The SP symbols are respectively transmitted once during 4 symbol periods in order of time according to one per three carriers. The SP symbols are transmitted during all symbol periods in frequency order according to one per twelve carriers.
A symbol described as “TMCC” in FIG. 2 indicates transmission of a TMCC (Transmission and Multiplexing Configuration Control) signal using a predetermined control information carrier. In the TMCC signal, a synchronous symbol indicative of synchronous timing of the frame is contained in the symbol numbers 1 to 16, a segment format identification symbol is contained in the symbol numbers 17 to 19, and a TMCC information symbol indicative of the type of segment, a modulating method and the like is contained in the symbol numbers 20 to 121. Incidentally, the control information carrier is defined so as to be modulated according to a DBPSK (Differential Binary Phase Shift Keying) system.
The symbols undescribed as “SP” or “TMCC” in FIG. 2 are used as data symbols that transmit broadcast main information.
In order to carry out such demodulation of ISDB-T, the TMCC signal receivable without using an equalizer is first received and the synchronous symbol contained in the symbol numbers 1 to 16 is detected, thereby establishing frame synchronism. Next, the corresponding pattern of SP symbols is detected in accordance with the established frame synchronism. Further, information about each SP symbol is received to detect a reference value used for signal equalization, thereby setting the equalizer.
However, the ISDB-T demodulating method has involved the following problems.
(1) While there is a need to establish the synchronism of the OFDM frame for the purpose of detecting each pattern of the SP symbols, the corresponding synchronous symbol in the TMCC signal must be detected to establish the synchronism of the OFDM frame. It is therefore necessary to receive 16 symbols or more corresponding to a synchronous symbol length for synchronous establishment.
(2) Since the TMCC signal is modulated based on the DBPSK system, there is a need to perform differential demodulation for its reception and there is hence a risk of degrading a synchronous characteristic.